1. Field of the Invention
The present invention relates to systems for distributed control, from generation to distribution with the supervision of the total power system by using a plurality of inter-linked actuators that include self-aware distributed impedance/voltage injection modules, energy storage devices, and other FACTS devices each having a high-speed (sub-cyclic) inter-communication capability and local control capability.
2. Prior Art
Most power utilities use energy management system (EMS) and supervisory control and data acquisition (SCADA) control systems to control HV power grid. These control systems connect and communicate between the power flow control units at the substations that are used to limit current flows or load imbalances over the HV power grid lines and provide interactive control of the power transmission on the HV power grid. Distributed and localized control of power flow, over the high voltage transmission lines using self-aware (with built-in capability to recognize problems/intelligence) distributed impedance (or equivalent voltage) injection modules (DIIMs) 102, has been proposed and is being implemented by the inventors of the current application as shown in FIG. 1 and FIG. 2. These DIIMs 102 are able to recognize changes in line current on the high-voltage lines, to which these are attached, and inject an appropriate inductive or capacitive impedance (alternately inject an equivalent voltage component) on to the line to locally balance the lines for power transfer.
Referring to FIG. 1 these self-aware (with built-in capability to recognize problems/intelligence) distributed impedance injection modules (DIIMs) 102 are distributed on segments of the high voltage (HV) transmission line 108, supported by, but insulated from, the towers 110, between the generation station 104 and the distribution points 106. These DIIMs 102 provide the capability of localized control of line current and line balancing for the local HV transmission line segment to which these are attached.
FIG. 2 provides a more detailed block diagram 200 of distributed control of the HV power grid by the DIIMs 102 injecting an impedance or equivalent voltage on the segments of the high voltage power transmission line 108 on which these are suspended. The HV power transmission lines are themselves supported by towers 201. The substations 204 with generation capability 203 and loads 205 are also shown. The overall control of the transfer of power between the generators and loads is monitored and controlled by a utility supervisory 206 that communicates with the substations via normal communication channels 207 for monitoring and control.
FIG. 2A is a block diagram 200A of the prior art implementation of controlling of the HV power grid using static synchronous series compensators (SSSCs) at the substations 204 that send information to the utility 206 and receive control instructions from the utility 206. The data and control are transferred over normal wired or wireless communication links 207 from SSSCs at the substations 204 to and from the utility 206. The generation capacity 203 and the distribution points 205 are connected to the HV power grid through the substations 204. The substations 204 are themselves enabled for power transfer over the high voltage (HV) transmission lines 108 suspended from the transmission towers 201.
FIG. 2B shows a block diagram 200B for prior art (U.S. Pat. No. 8,401,709) local control of the HV power grid using existing resources proposed by the identified prior art Cherian applications and patents. These implementations are for unified power system control from the main generation 203 and distributed generators 213-1 and 213-2 (wind, solar, etc.) to distribution loads 205-1 to 205-3 connected by local power distribution lines 109, by local control modules 215-1 and 215-2. The control of the power system is proposed by controlling the existing assets at the substations 204-1 and 204-2 by using regional control modules 225 at the substations 204-1 and 204-2, using centralized computer programs at the enterprise control module 206, with generation and distribution connections to the HV power grid system. Such a system has been proposed by the Cherian applications, where data visualization programs 280 with smart grid control programs 285 use system modeling and simulation capability 290 at the enterprise 206. The proposed power system of control uses existing wireless area network (WAN) connections 230 to communicate with the various substations and for communication between the substations 204-1 and 204-2 and the enterprise control.
In order to improve the performance of the existing HV power grid flexible alternating current transmission system (FACTS) devices are being employed within, at the edge and outside the edge of the HV power grid. These FACTS devices are typically high-voltage compatible subsystems that are coupled directly to the HV power grid even though in certain circumstances the physical connection may be at the MV (medium-voltage) level. The devices and systems include the static synchronous series compensators (SSSC)], static synchronous compensators (STATCOMs), unified power-flow controllers (UPFCs), interline power-flow controllers (IPFCs) and other electronic systems for monitoring and control, typically connected at the sub-stations and in communication with the utility over normal communication channels to send data and receive control instructions. All these prior art implementations aid in maintaining and enhancing grid resiliency and power system stability through local VARs support and power-flow control of the prior art HV power grid.
The recent advances in distributed non-conventional generation, such as wind and solar energy systems, due to their respective uncertain natures, coupled with the cyclic nature of consumer demand for power, have made the optimization of power flow over the HV power grid from generation to distribution difficult. These random inputs and outputs to and outputs from the HV power grid have also made the HV Power grid more prone to disturbances, that result from sudden changes in supply or load that can disrupt the operation of the HV Power grid. These disturbances include small signal instability, power oscillations and sub-synchronous resonance among others. If left uncorrected these can grow and affect the overall operational stability of the HV power grid and the total power system. Hence the new HV power grid and the total power system require different and faster capabilities for line balancing and for overcoming disturbances introduced by the distributed nature of power generation and load changes. It is essential to improve the response capability of the HV power grid control in order to take care of the changed nature of the HV power grid and the total power system and its characteristics.
The problems to be addressed in this regard include balancing of lines when new distributed generation systems or loads come online and respond to disturbances. Due to the new nature of the HV power grid, such as responding to small signal stability issues, power oscillations damping (POD) and sub-synchronous resonance (SSR) damping on the HV power grid requires response at faster speeds to overcome more of these problems. The implementation of distributed energy storage capabilities that are coupled to the HV power grid will also have to be brought in and integrated to help in improving the stability of the HV power grid and the total power system as it is made more responsive to power changes on the HV power grid. Thus, it will be useful if the capability is established whereby responses to changes or disturbances on the HV power grid can be addressed locally, at appropriate speeds, in a hierarchical and integrated fashion and resolved using all the available capabilities and resources that exist, working in coordination. It will be of even further advantage if the total power system from generation to distribution can be brought together under an integrated and dynamic communication and control capability to enhance the stability and response to disturbances of the total power system.